Re: [PATCH] Dynamic growable arrays for internal use

[Florian Weimer <fweimer at redhat dot com>]

On 06/06/2017 05:30 PM, Stefan Liebler wrote:
> Hi Florian,
> 
> I get the following warning / werror with gcc 4.8.5 on s390x:
> gcc tst-dynarray.c -O3 -c ... -o <build>/malloc/tst-dynarray.o
> In file included from tst-dynarray.c:50:0:
> tst-dynarray.c: In function ‘do_test’:
> ../support/check.h:51:8: error: ‘result.length’ may be used
> uninitialized in this function [-Werror=maybe-uninitialized]
>      if (expr)                                                   \
>         ^
> tst-dynarray.c:377:23: note: ‘result.length’ was declared here
>      struct long_array result;
>                        ^
> In file included from tst-dynarray.c:50:0:
> ../support/check.h:51:8: error: ‘result.array’ may be used uninitialized
> in this function [-Werror=maybe-uninitialized]
>      if (expr)                                                   \
>         ^
> tst-dynarray.c:377:23: note: ‘result.array’ was declared here
>      struct long_array result;
>                        ^
> cc1: all warnings being treated as errors
> 
> 
> Have you seen those warnings on other architectures, too?

I could reproduce it with -O3 on s390x.  I have not tried it with other
architectures, but it is a generic problem with TEST_VERIFY_EXIT which
is not really related to the dynarray code.  I propose the attached
patch to fix it.

Thanks,
Florian

support: Expose TEST_VERIFY_EXIT behavior to GCC optimizers

Previously, the implementation would conditionally exit based on the
status argument, which GCC did not know about.  This leads to
false uninitialized variable warnings when data is accessed after a
TEST_VERIFY_EXIT failure (from code which would never execute).

2017-06-07  Florian Weimer  <fweimer@redhat.com>

	Expose TEST_VERIFY_EXIT process termination to GCC optimizers.
	* support/support_test_verify_impl.c
	(support_test_verify_exit_impl): Split from
	support_test_verify_impl.
	* support/check.h (TEST_VERIFY): Drop status argument from
	support_test_verify_impl call.
	(TEST_VERIFY_EXIT): Call support_test_verify_exit_impl.
	(support_test_verify_impl): Remove status argument.
	(support_test_verify_exit_impl): Declare.

diff --git a/support/check.h b/support/check.h
index 1d244a3..bdcd129 100644
--- a/support/check.h
+++ b/support/check.h
@@ -51,7 +51,7 @@ __BEGIN_DECLS
     if (expr)                                                   \
       ;                                                         \
     else                                                        \
-      support_test_verify_impl (-1, __FILE__, __LINE__, #expr); \
+      support_test_verify_impl (__FILE__, __LINE__, #expr);     \
   })
 
 /* Record a test failure and exit if EXPR evaluates to false.  */
@@ -60,7 +60,8 @@ __BEGIN_DECLS
     if (expr)                                                   \
       ;                                                         \
     else                                                        \
-      support_test_verify_impl (1, __FILE__, __LINE__, #expr);  \
+      support_test_verify_exit_impl                             \
+        (1, __FILE__, __LINE__, #expr);                         \
   })
 
 int support_print_failure_impl (const char *file, int line,
@@ -70,8 +71,11 @@ void support_exit_failure_impl (int exit_status,
                                 const char *file, int line,
                                 const char *format, ...)
   __attribute__ ((noreturn, nonnull (2), format (printf, 4, 5)));
-void support_test_verify_impl (int status, const char *file, int line,
+void support_test_verify_impl (const char *file, int line,
                                const char *expr);
+void support_test_verify_exit_impl (int status, const char *file, int line,
+                                    const char *expr)
+  __attribute__ ((noreturn));
 
 /* Record a test failure.  This function returns and does not
    terminate the process.  The failure counter is stored in a shared
diff --git a/support/support_test_verify_impl.c b/support/support_test_verify_impl.c
index 5bae38f..55ab211 100644
--- a/support/support_test_verify_impl.c
+++ b/support/support_test_verify_impl.c
@@ -22,12 +22,16 @@
 #include <stdlib.h>
 
 void
-support_test_verify_impl (int status, const char *file, int line,
-                          const char *expr)
+support_test_verify_impl (const char *file, int line, const char *expr)
 {
   support_record_failure ();
   printf ("error: %s:%d: not true: %s\n", file, line, expr);
-  if (status >= 0)
-    exit (status);
+}
 
+void
+support_test_verify_exit_impl (int status, const char *file, int line,
+                               const char *expr)
+{
+  support_test_verify_impl (file, line, expr);
+  exit (status);
 }